360 running on 4 cylinders

You won't really know the extent of what the engine needs until you take it apart. Maybe just a refresh of bearings and rings. Maybe a complete overhaul.
I've lost complete confident in the PO's abilities. It was supposed to have been rebuilt but never run (still had assembly lube in the plug holes, etc.) We found so much stuff that was done wrong, timing chain installed 40 degrees out, wrong transmission (early 60's 904 that didn't mate up to the engine), various other electrical problems, took me and my son almost 2 years to get it running and safe. At this point, I'm almost sure we'll uncover more bad/wrong stuff inside it.